This invention relates generally to shrink wrap packaging and particularly to an improved package of this type which is ventilated to provide for air circulation for the package contents.
The use of plastic film such as that sold under the trademark Saran is well-known for use in shrink wrap packaging and is described in U.S. Pat. No. 3,034,271. This patent discloses an apparatus in the form of a heated tunnel by which the shrinking of a transparent plastic wrapping disposed about a container of fruit and the like is accomplished. Such packaging has the advantage of allowing the fruit to be visible and protected from contamination by dust and by customer handling. It has, however, the disadvantage of effectively encasing the produce in a sealed container of air which, in the case of fruit, vegetables and other footstuffs results in shortened shelf life. The reason for this is that fruit, for example, generates ethylene which promotes accelerated ripening. One approach to overcoming this problem, is disclosed in U.S. Pat. No. 4,515,266 in which untreated (i.e. non-shrunk) plastic sheet is formed into packages, and the air is evacuated and replaced with an inert preservative gas such as argon. The plastic sheet is perforated with very small openings which permit a slightly positive gas pressure to exist within the package but which are specifically chosen to prevent inflow of air into the package.
The use of plastic packaging having relatively large openings for the expulsion of air is well known but such openings are intended to facilitate the packaging of bulky and compressible articles such as blankets, clothing and the like to facilitate the rapid release of entrapped air. Indeed, without such openings thses articles would be very difficult to handle.